* cuda: fuse FFN gate/up and GLU in MMQ with interleaved gate/up rows
For prompt processing, run the gate and up matmuls of a dense FFN as one
mul_mat_q launch and apply the GLU in the write-back.
- The loaders take the gate weights as a second pointer and fill the weight
tile with up and gate rows interleaved in chunks of 8, so each thread holds
an up value and the matching gate value (rows r and r + 8 of an MMA tile).
- The MMA loop is unchanged: same tile, warp layout, vec_dot and one sum[]
per thread. The fused write-back computes the GLU from registers and writes
half the rows.
- The fused path uses the regular tiling (no stream-k) with the column tiles
innermost so that neighbouring blocks share weight tiles.
- Enabled for Q4_K, Q5_K, Q6_K, Q8_0 and IQ4_XS on NVIDIA Turing and newer.
* cuda: assert the fused MMQ gate argument and trim redundant comments
* cuda: move the fused MMQ hint check to should_fuse and add TODOs
* cuda: pass prec_src1 to the fused MMQ write-back
* cuda: fuse only with efficient tiling and no fallback, merge the GLU write-back
* cuda: require has_fusion explicitly, drop the fusion-only src1 precision check
* cuda: launch the fused MMQ kernel through the stream-k kernel with one block per tile
* cuda: inline the MMQ tiling-efficiency check
* tests: one fused gate/up MMQ case per type and GLU op
* cuda: always launch the fused MMQ kernel with one block per tile
* tests: shorten the fused gate/up MMQ test comment
* cuda: select the fused MMQ loader and write-back in ggml_cuda_mmq_get_util_funcs
* cuda: run the fused MMQ kernel on the plain tiling path
* cuda: put the column tiles innermost in the MMQ plain tiling path